We wish to understand on a molecular level enzyme catalysis in which molecular oxygen is cleaved and incorporated into organic substrates. It is our belief that enzymes catalysis is affected by every level of enzyme structure and therefore cannot be "understood" by any one technique designed to probe a single level. On the contrary, a diversity of approach is mandatory. We have thus described a systematic application of sensitive chemical and physical techniques including: Optical, IR, ENDOR, NMR, Mossbauer and EPR spectroscopy, chemical modification of proteins, determination of protein sequence and measurement of low temperature, steady state and presteady state kinetics. We have chosen for study a representative group iron containing mammalian and bacterial dioxygenases and monoxygenases of environmental and metabolic significance. These include 1) Kidney 3-hydroxyanthranilate dioxygenase; 2) P. aeruginosa and B. fuscum 3,4 protocatechuate dioxygenase; 3) P. testosteroni 4,5 protocatechuate dioxygenase; 4) P. putida 1,2 catechol dioxygenase; 5) P. putida cyt. P450cam monoxygenase; and 6) human placental cytochrome P450 monoxygenase. Each protein will be purified and characterized in terms of 1) molecular parameters; 2) iron content and state; 3) reaction cycle intermediate; 4) resonance spectral properties; 5) dynamic and thermodynamic parameters. Selective modifications will then be made in the protein, its substrate or its environment and the proteins recharacterized. Our goals are 1) to formulate reasonable and defensible mechanisms at the atomic level; 2) to identify the form of oxygen which reacts with substrates; 3) to understand the role of iron in these metalloproteins; 4) to understand the bearing on catalysis of protein interactions with other proteins, solvent and membranes; and 5) to extend theory by making careful measurements on well defined systems. We have used this approach in past studies to propose mechanisms for both mono and dioxygenases.